Subaru Legacy Forums

Subaru Legacy Forums (
-   Turbo Powertrains (2.0GT, 2.5GT, 2.5XT) (
-   -   Help Request: AVCS Related Problem (

Underdog 02-19-2010 10:48 AM

Help Request: AVCS Related Problem
Warning: This is a lengthy post, but I kept it as concise as possible. I have spent almost two months chasing down this problem and need some feedback.

It all started a few days after finishing my engine rebuild. I had driven the car three or four times, maybe about two hours total, when I got a P0021 DTC. This trouble code is associated with a mechanical problem with the AVCS - Bank 2. Around the same time, but not exactly the same time, my low oil pressure light came on. As it turns out, the pressure relief valve on my oil pump was sticking open, causing low pressure... no problem, a new oil pump fixed the low pressure light and it seemed I'd caught the problem before any damage was done. Since one of the things to check for P0021 is oil pressure, I assumed I was fixing both problems.

Unfortunately, a few days after putting in the new oil pump and clearing the ECU my P0021 DTC returned. I searched the forum and found many people have had faulty oil control valves (OCV) with this DTC. Again, this was a component to be inspected per the diagnostic procedure so I removed the driver-side OCV, cleaned it, and reinstalled it. When the problem came back two consecutive starts later, I decided to swap the OCV with the other side. Unfortunately, by monitoring the DTC as well as the VVT advance and OCV duty cycle, it was apparent that the problem did not switch sides, ruling out a faulty OCV. Also there are codes associated with the circuitry for the OCVs, opens/shorts in the circuity are P2088-2093.

My next step was to verify that there was oil pressure at the OCV, to rule out a blockage upstream, but after the oil sender port. By cracking the bolt loose on top of the OCV I was able to see that the oil had quite a bit of pressure, even at idle.

Then I tried swapping the cam position sensor with a known good one. This was a reach, but the last thing I could think to check before pulling the motor. Why a reach? The cam position sensor output is a square waveform generated by a hall effect sensor and slot on the camshaft. If the sensor was bad, it would trigger another code like P0340 or P0345 which relates to the electrical performance of the cam position sensors.

With all those components checked, I had two weeks of driving before I would have the opportunity to pull the motor. I drove my normal commute every day and monitored the OCV duty cycle and VVT advance. The DTC/CEL would come and go, although my driver-side VVT advance would fluctuate randomly between 0-3* while the passenger-side would go between 0-35* and seemed to be not random, moving only when the system would call for it. During this time there was no bucking/hesitation/stalling or rough idling... the symptoms were only evident through DTC/CEL and monitoring the engine parameters.

Two days ago I pulled the motor so I could inspect the passages in between the OCV (built into cam cap) and the camshaft, as well as the passages in the camshaft, and the sprocket itself. I checked the banjo bolt... absolutely clear. All the passages in the cam cap were clear, as was the camshaft, and the oil feed pipe (as you would expect given the banjo bolt filter).

Now I'm wondering if the VVT mechanism in the sprocket is sticking... For some reason when I reset the ECU and start the engine cold both sides of the engine start at 5* advance. Over the next ten minutes of driving, both sides will seem to function properly, but the driver-side will slowly drift to a higher offset than the passenger-side. When I come to a complete stop both sides go to zero and then the driver-side never recovers.

When I try resetting the ECU and starting with the engine warm, both sides start at zero and the problem is consistent. When I start the engine cold, but haven't reset the ECU the problem is consistent. There is something special about the combination... my guess is maybe after a ECU reset the default position is 5* and the high oil pressure of a cold start helps dislodge the VVT mechanism?

So at this point the motor is partially apart on my engine stand. I'm thinking I should just replace the sprocket to rule that out ($130... ouch). What I'd like is to get any additional ideas from the experienced forum members.

Again, sorry for the wall of text. :redface:

JoeFromPA 02-19-2010 10:55 AM

UD - That was pretty concise for the explanation into it. I have nothing to offer here in terms of expertise...but I have to ask: Are you running shell rotella t 5w40 synthetic? Might be your problem right there, if not.


Can't wait to see this love affair get off the rocks.

GTTuner 02-19-2010 04:46 PM

As I was reading your delima and thinking of what you could be missing here and the sprocket was the first thing I thought of. I read on and you mentioned it. I think you are on the right track. Here is my initial thought; Are the sprocket part numbers the same for both banks? That would be the only way I can think of to not spend the money and test if that is the problem. My cam sprockets are buried in the trunk of my car so I cant check them, otherwise I would go out there right now.

rao 02-19-2010 05:37 PM

At some point, if there are no blockages, nothing wrong with the oiling system and no electronic problem, the likely culprit if the gear itself. I suppose if you took the gear off and apart it may hold some clues, but the odds aer it will look just fine.

Unfortunately you won't really be able to tell until you replace the parts, put the engine back together and put it back in the car.

BTW, what kind of oil were you using when this all happened? and what OCI?



I hope you sort it out soon.

GTTuner 02-19-2010 05:44 PM

^^^^ Shit stirrin bastard. :lol:

Underdog 02-21-2010 09:21 AM

GTTuner: The sprockets are not the same unfortunately... The passenger side and the driver side are not in the same plane because of the offset of the cylinders. As a result the passenger side sprockets are "behind" the mating surface of the camshaft, and the driver side are in front. Hard to explain.... see the pic below.

Thanks for the feedback guys... I guess I'll just have to replace the sprocket while I'm in there.

To answer mwiener2's question from my rebuild thread, I have pinned out the engine harness between the main connector and the OCV connector and everything was well within spec. I should still check between the ECU and the main connector, but if there was an open or short in the circuitry it should be giving me a P2092 or P2093 code. Also, logging duty cycle and amperage to the OCV shows that it is drawing current.

Let's see... I rebuilt the motor at 60,900mi, changed the oil after the first 30 mins of idle/warmup, changed the oil twice as part of diagnosing this problem, and am changing it again at 61,800mi due to removing the valve cover and installing the STi gauge pack. So on average that's a 250mi OCI using Castrol GTX 5W-30. :lol:

GTTuner 02-21-2010 10:53 AM

I am almost 100% positive you have a proper diagnosis on this. What else is in the system? Nothing really, good luck.

mwiener2 02-21-2010 05:48 PM

It's a bad ECU!!!!!! :eek::spin:

unclemat 02-21-2010 05:59 PM

I'd say swap the cam sprocket.

GTTuner 02-21-2010 06:28 PM

Take the sprocket apart, what do you have to loose?

Underdog 02-21-2010 08:57 PM

I'm going to order the sprocket in the morning... I'll need to get a set of Torx Plus bits to take the old sprocket apart, that's the only thing stopping me at this point.

Sweet jeebus I hope it's not a bad ECU. I think you are joking mwiener but it has definitely crossed my mind. The only comfort I have is seeing the duty cycle and current for the OCV behaving normally. After the cam sprocket, I can only go upstream to the ECU for an electrical issue.

Underdog 02-22-2010 08:37 AM

For reference, the sprocket part numbers are 13322AA001 (driver-side) and 13320AA001 (passenger-side) and they go for about $200 through a dealer, but our forum vendors FredBeans and will sell them for ~$140.

It looks like I won't be able to disassemble the sprocket without drilling out the bolts. They are a five-lobed star design which is different from the six-lobed Torx and Torx Plus... they are "tamper-resistant" Torx Plus.

The tamper-resistant Torx Plus can be found with or without the post in the center, but either way the tool is only manufactured by two companies and they only sell them to service companies or OEMs.

unclemat 02-22-2010 08:41 AM

You can easily buy tamper resistant Torx Plus online.

Underdog 02-22-2010 08:46 AM

Yeah, I'm seeing that now... so weird that the customer service rep at camcar said it is illegal for them to sell to individuals. Not sure I want to get a $100 set of these to satisfy my curiosity, I'll just have to poke around and find a deal.

rao 02-22-2010 08:46 AM

+1 I have a full set of Torx Plus tamper-resistant bits :)

All times are GMT -6. The time now is 11:20 PM.

vBulletin Optimisation provided by vB Optimise v2.6.3 (Lite) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.